Fluidic thread break detection device and system

ABSTRACT

The application discloses an improved thread break detection device and system, intended particularly for use in industrial sewing equipment, which makes advantageous use of fluidic control components and circuits. The utilization of fluidic systems for thread break detection and the control has been known to be theoretically desirable, but its practical accomplishment has been elusive. The disclosed system includes a unique yet extremely simplified thread sensing fluidic control device, in advantageous association with known fluidic control elements, to achieve fluidic control of thread break detection with a high level of practicality. The system utilizes a wire-like thread detecting element of rather conventional configuration but arranged in a unique manner to provide system pressure variation in response to thread break. A fluidic position sensor element is arranged to sense a slight back pressure increase occasioned by movement of the sensing wire and to effect the desired machine control in accordance therewith.

Dec. 2, 1975 1 FLUIDIC THREAD BREAK DETECTION DEVICE AND SYSTEM [75] lnventor: Francis H. Hughes, North Troy,

[73] Assignee: Cluett, Peabody & Co., Inc., New

York, N.Y.

[22] Filed: Mar. 8, 1974 [21] Appl. No.: 449,383

[52] US. Cl. 112/218 R; 112/219 B; 116/65; 139/370 [51] Int. Cl. D05B 69/36; B65H 63/02 [58] Field of Search 73/160, 37.7; 116/65; ZOO/61.18, 81.9 R; 137/829, 832; 139/351, 139/370; 28/51; 112/218 R, 219 B; 242/37 R [56] References Cited UNITED STATES PATENTS 829,208 8/1906 Hayes et a1 112/219 B 2,752,444 6/1956 Vossen ZOO/61.18 2,944,558 7/1960 Dodge ZOO/81.9 R 3,285,608 11/1966 Lyman.... 73/37.7 3,335,737 8/1967 Gesell 1. 137/832 X 3,672,315 6/1972 Rockwell 242/37 R 3,695,283 10/1972 Ringwall 137/829 X 3,769,475 10/1973 Czwakiel ZOO/81.9 R

3,834,634 9/1974 Havlas et a1. 242/37 R X Primary ExaminerRichard C. Queisser Assistant ExaminerDaniel M. Yasich [57] ABSTRACT The application discloses an improved thread break detection device and system, intended particularly for use in industrial sewing equipment, which makes advantageous use of fluidic control components and circuits. The utilization of fluidic systems for thread break detection and the control has been known to be theoretically desirable, but its practical accomplishment has been elusive. The disclosed system includes a unique yet extremely simplified thread sensing fluidic control device, in advantageous association with known fluidic control elements, to achieve fluidic control of thread break detection with a high level of practicality. The system utilizes a wire-like thread detecting element of rather conventional configuration but arranged in a unique manner to provide system pressure variation in response to thread break. A fluidic position sensor element is arranged to sense a slight back pressure increase occasioned by movement of the sensing wire and to effect the desired machine control in accordance therewith.

6 Claims, 3 Drawing Figures FLUIDIC THREAD BREAK DETECTION DEVICE AND SYSTEM BACKGROUND AND SUMMARY OF INVENTION Automatic or semi-automatic industrial sewing equipment typically is provided with automatic thread break detecting means capable of sensing the presence or absence of an intact thread disposed along a predetermined guide path. Superficially, thread break detection would appear to be a simple problem, solvable by placing a biased detecting element in contact with the thread, which is guided along a predetermined path between spaced guides or supports by reason of a certain amount of tension being maintained on the thread. If a thread break occurs, the tension in the thread system is relieved, and the detecting element can move toward its bias position to effect a control response. While the problem and solution is simple in concept, it proves to be difficult in practice, for several reasons. For one thing, it is desired to maintain the thread supply system under accurately controlled thread tension, and so the design of the thread break detector must be such as to avoid imposing any non-uniform frictional drag on the moving thread. For another, the thread break detection system operates in a rather hostile environment, in that there is typically considerable lint in the area of the sewing operation,'which can cause irregular operation of lightweight, sensitive mechanisms. Thus, notwithstanding the availability of a variety of devices and systems for the purpose of detecting thread break in industrial sewing operations, a need for improvement has remained.

DESCRIPTION OF PRIOR ART One form of thread break detector in common use prior to the present invention is that described in the Vossen US. Pat. No. 2,752,444. The detector element of that system is a lightweight wire, with a downwardly opening hook arranged to be suspended by a properly guided and tensioned thread. The wire is biased downwardly only by its own weight, which is minimal, and is arranged so that its lower ends hang slightly above pools of mercury, constituting electrical terminals of a switch. When a thread break occurs, the wire is dropped from its suspended position, its ends are immersed in the mercury pools, and an electrical circuit is completed through the wire itself to effect the necessary control functions. The device of the Vossen patent has interesting advantages in terms of mechanical simplicity,.minimum effect on thread tension control, etc. However, the need for mercury pool switch contact elements introduces significant problems.

Among these problems is the fact that the open mercury pools can give off highly toxic vapors and this can present a health hazard to the machine operator. The mercury pool device also has a significantly higher initial cost (e.g., almost twice the initial cost of the fluidic device of the invention). ln operation, the mercury pool device is subject to mercury spillage, which not only renders the device inoperative (possibly without the knowledge of the machine operator), but also creates a possibility of causing a short circuit if the escaped mercury comes into contact with other portions of the control system. Even when otherwise operating normally, the mercury pool device is subject to fouling and intermittent malfunction resulting from accumulations of lint. In this respect, it will be understood that there is considerable airborne lint in the vicinity of an industrial sewing machine to which the machine components are necessarily exposed.

It has also been proposed in the prior art to utilize fluidic controls systems for thread break detection, and one such proposal has involved suspending on the guided and tensioned thread a wire loop supporting a valve plug over its socket. Upon occurrence of a thread break, the valve plug is intended to drop into its socket, shutting off an air passage and thus initiating a desired control function. This system, while conceptually interesting, requires excessive weight to be applied to the thread, introduces variable tension factors, and requires expensive components. Thus, while the fluidic control has important theoretical advantages, such as a self-cleaning tendency derived from the flow of air in the vicinity of the critical parts and the avoidance of electrical power in exposed areas of the equipment, it has not been practical heretofore to utilize fluidic systems for practical industrial thread break detection.

SUMMARY OF THE INVENTION In accordance with the present invention, the desirable and advantageous features of the prior art proposals are adapted and combined in a unique and advantageous manner, to provide a highly simplified and entirely practical fluid thread break detection system for utilization in an industrial environment. To this end, the system of the present invention incorporates a lightweight, substantially frictionless sensing element, in the form of inverted U-shaped wire similar to that shown in the beforementioned Vossen patent. However, in the system of the present invention, the lightweight wire detecting element is not associated with the mercury pools of the Vossen patent, but is arranged, when dropped by a broken thread, to at least slightly impede flow of control air through the detecting device. Importantly, the wire-like sensing element is not utilized as an on-off valve, but only as a relative restriction and thus can be guided and received in a control body in a substantially friction free manner.

Associated with the detecting device, in the system of the invention, is a position sensor fluidic device, which may be of conventional, commercially available design. The position sensor device is actuated from a first output condition to a second output condition in response to sensing a slight increase in back pressure on the upstream side of the thread break detecting device, as will occur when the wire-like detecting element is dropped into its relatively flow obstructing position. The change in output condition of the 'position sensor is utilized through more or less conventional forms of fluidic circuitry to achieve the desired control function in response to the thread break.

A significant advantage of the detector device of the invention is its self-purging or self-cleaning characteristic, as regards airborne lint. Thus, while exposure to the lint cannot easily be avoided, the constant flow of sensing air through the device, and through the substantial clearance spaces provided therein, makes the device substantially resistant to lint fouling. Thus, the device of the invention provides for greater reliability in operation, at a lower initial cost, and without the health hazards of other complications inherent in the use of more conventional mercury pool devices.

Thus, the system of the invention is characterized by exceptional simplicity and reliability, enabling fluidic circuitry to be extended in a practical manner to thread 3 break detection.

For a better understanding of the above and other features and advantages of the invention, reference should be made to the following detailed description of a preferred embodiment, and to the accompanying drawings.

DESCRIPTION OF THE DRAWINGS DESCRIPTION OF A PREFERRED EMBODIMENT Referring now to the drawing, and initially to FIGS. 2 and 3 thereof, the reference numeral represents the body portion of the detecting device. The body portion may be formed of metal or suitable plastic material (typically the latter). It is secured to a subplate 11 by means of mounting bolts 12, and the subplate itself is in turn secured in an appropriate location to the sewing machine by bolts 13.

In accordance with one aspect of the invention, the detector body 10, in its mounted position, is provided with at least one, and more advantageously two vertical passages, 14, 15 for the reception of the downwardly extending vertical leg portions 16, 17 of a detecting wire, generally designated by the reference numeral 18. The detecting wire 18 is of generally inverted U-shaped configuration, and typically may be formed of stiff wire of around 0.030 inch in diameter. This wire size is, of course, not critical, but has been found suitable. Overall lightness in weight is a desired objective; as is a reasonable degree of stiffness andstrength to withstand the necessary handling of the wire for threading and other operations.

In the device illustrated in FIG. 2, the vertical bore 14 may be considered as the primary bore, and its diameter is substantially larger than that of the wire leg 16, in order to permit the free and substantially frictionless vertical movement of the wire leg 16 within the bore. At the same time, the relationship of the wire diameter and bore diameter, in the bore 14,'should be such as to relatively impede, but not completely restrict, air flow in the passage, between the wire and bore walls, causing an appropriate pressure differential resulting in a low efficiency restriction. In practice, a bore diameter of about 0.052 inch has been found suitable for cooperation with a wire diameter of about 0.030 inch.

In the illustrated device, the body 10 is provided with a second and larger vertical bore 15 for reception of the wire leg 17. For the purposes of the present invention, the bore 15 may be substantially larger in diameter than that of the bore 14, as the bore 15 functions solely to provide unrestricted and substantially friction free gross guidance for the wire leg 17 and has no substantial functions with respect to air flow considerations. For this purpose, it has been found suitable to utilize a diameter of around 0.093 inch for the vertical bore 15. To advantage, both of the bores 14, 15 may be 4 relieved at their upper ends by larger diameter counter bores 19.

As reflected in FIGS. 2 and 3, the upper end of the detecting wire 18 is provided with a connecting portion 20 which is bent downwardly to form spaced, thread receiving bight regions 21, 22. The arrangement is such that the wire detecting element may be suspended from a thread T received in the bight portions 21, 22. In this respect, it will be understood that the geometry of the Wire detecting element 18 is such that, when it is suspended by the thread T, its weight balance will be such that the legs 16, 17 hang downward at a 0 or near 0 angle to the vertical, so that the depending wire legs do not become significantly canted with respect to the vertical bores 14, 15 in the detector body.

Suitable thread guiding means 23 are provided on opposite sides of the wire detecting element 18. In the illustrated arrangement, the thread guides are mounted directly on the subplate 11, in a position spaced a predetermined, desired distance above the detector body 10. The threaded guides are positioned to provide a relatively short unsupported span of thread in the region of the wire guide 18 such that, when the thread is passing through the guides under the desired operating tension, the lightweight wire element 18 will be suspended by the thread at a desired level in relation to the detector body 10. A retaining wire 24 projecting outward from the subplate 11, serves to retain the wire 18 against accidental dislodgement from the body 10.

In accordance with the invention, the detector body 10 is provided with a through bore 25, which extends transversely through the body portion 10, in intersecting relation to the primary vertical bore 14. In the illustrated arrangement, the through bore also intersects the secondary vertical bore 15, but that is a function of convenience in the machining operations and is not necessary to the operation of the device. At its end adjacent to primary vertical bore 14, the through bore 25 is provided with a tapped counterbore 26 receiving a fitting 27 connected to an air supply tube 28.

When the system is in operation, air is supplied through the tube 28 at low pressure (e.g., about 5 psig). In general, the control air thus supplied is permitted to escape directly through the air passage 25, although some of it can also escape through the open ended vertical bores 14, 15. When the wire detecting element 18 is suspended on a thread T, properly tensioned and guided by the element 23, the lower end extremity 29 of the wire leg 16 is located slightly above the air passage 25, such that the detecting element has substantially no effect upon the flow of control air through the passage 25. At such time as a break or other discontinuity occurs in the thread T, the wire element 18 is permitted to drop by gravity, until the connecting portion 20 engages the upper surface 30 of the body portion 10.

In accordance with the invention, the spacing of the thread guide element 23 above the body portion 10 is somewhat greater than the spacing of the lower end extremity 29 of the wire leg 16 above the control air passage 25. Accordingly, when the wire element is dropped, as reflected in broken lines in FIG. 2, the wire leg 16 drops to a position in which it passes transversely through the control air passage 25. The diameter of the control air passage 25 most advantageously is approximately the same as that of the primary vertical passage 14 (0.052 inch in the illustrated device). It could be somewhat smaller in diameter, but should not be significantly larger.

When the wire detector element 18 is dropped into its lower or flow impeding position, the flow of control air through the passage 25 is relatively impeded, but not stopped, by the presence in the passage of the somewhat smaller diameter wire. As will be readily appreciated, when this occurs, a slight increase in control air pressure occurs upstream of the obstruction, or in the air tube 28.

In normal operation, with the detecting element 18 properly suspended on a properly tensioned thread, a predetermined flow of air through the tubing section 28 and through the control air passage 25 will result in a predetermined back pressure in line 28. When the air flow is reduced by the presence of the wire leg 16 athwart the passage 25, the reduced flow is reflected in a slight increase in the back pressure existing upstream of the detector device.

In accordance with the invention, the control air line 28 is connected to the sensing port 33 of a fluidic position sensor device 34. The position sensor device may be of a conventional, commercially available type, such as Corning Part No. 192433, available from Corning Glass Works, Corning, New York. This position sensor device is provided with an air input 35 and output 36, together with the sensing port 33. The operation of the position sensor device 34 is conventionally such that, with a predetermined, normal air flow being passed through the sensing port 33, supply pressure is caused to be directed to the output 36, maintaining an output pressure line 38 in a normally pressurized condition. When a slight increase in pressure occurs in the line 28, the increased pressure is detected at the sensing port 33 of the position sensor, and this causes the air fiow within the sensor to be diverted from the normal output 36, relieving the pressure from the line 38. Significantly, the position sensor device is capable of responding to a pressure increase at the sensing port 33 of as little as 6%. Accordingly, even though the detecting wire 18 is only loosely and freely received within the primary bore 14, and only partially impedes the flow of control air through the supply line 28 and passage 25, such relative flow impedance can be detected by the position sensor, and a dicisive control function derived therefrom by the release of pressure from the line 38.

In a typical industrial sewing machine thread break detecting system according to the invention, there may be provided a pair of thread break detecting devices, each associated with a position sensor fluidic device 34. The normally pressurized output line 38 of each position sensor device is connected to a control pair input of a so-called NOR/OR fluidic device 39, each having a normally non-pressurized output 40, 40a. The respective outputs 40, 40a constitute control air inputs to a fluidic flip-flop device 41 having outputs 42, 43. The NOR/OR devices 39 are, in a typical circuit, provided with a second, normally non-pressurized control input through lines 44 and control device 45, for control purposes unrelated to the present invention.

Thus, in the system of FIG. 1, if there is a break or other discontinuity in either of the threads T1 or T2, the related detecting wire will be dropped, a slight increase in control air pressure will be sensed by the position sensor fluidic device, whose output line 38 will then be relieved of its normal control pressure. The associated NOR/OR control, then sensing no pressure in either of the lines 38, 44 will devert its input pressure into the normally non-pressurized output lines 40 or 40a. When the flip-flop device 41 senses pressure in either of the lines 40, 40a, its input pressure is diverted to its outlet 43, causing the actuation of a pressure switch 45. The pressure switch 45 is utilized to derive all of the desired control functions, such as declutching and/or shutting off of the sewing machine, actuating the necessary visual or audible alarms, etc.

The nature of the flip-flop device 41 is such that it is returned to its initial or normal operating condition only by the application of control pressure to an input 46. Typically, this is achieved through a manual reset valve 47 connected through a line 48 to the flip-flop input 46. When the line 48 is pressurized, the flip-flop output 43 is depressurized, while the output 42 is pressurized, permitting the sewing equipment to be returned to the operating condition.

The system of the invention, utilizing a unique and advantageous combination of a lightweight, loose-fitting, thread engaging element as a low efficiency flow restricting device, in conjunction with a position sensor fluidic device which is highly sensitive to pressure variations, provides a reliable and wholly practical arrangement for utilizing fluidic control for thread break detection. In this respect, while the theoretical aspects of applying fluidic control to thread break detection seem rather evident, the practical application of such controls has remained elusive, because of the special requirements inherent in the thread detecting operation. Among these are that the influence of the thread sensing elements on the thread itself must be both minimal and uniform. In the system of the present invention, this is realized by the utilization of a simple, lightweight wire element, which is normally suspended on the intact thread, but which provides for controllable low efficiency restriction in the fluidic system. The use of such lightweight wire elements is known and of proven effectiveness in prior (non-fluidic) systems, such as reflected in the Vossen patent, for example, and the present invention makes possible and practical the use of such elements in a fluidic control system. To advantage, the wire-like element is of an inverted U-shaped configuration, providing at its upper end a pair of spaced, downwardly facing bight portions for engagement with a properly tensioned thread. Engagement of the wire element by the thread at two spaced points avoids any tendency of the wire element to rotate or otherwise change its orientation relative to the thread, which could result in an undesired variation in thread tension.

A significant aspect of the invention involves the use, in conjunction with the above described, restrictionforming detecting device, of a position sensor fluidic device, rather than a regular back pressure sensing device. While a conventional back pressure sensing device requires a significant variation in back pressure to achieve reliable control effects, the position sensor device, used in the capacity of a back pressure sensing means, is reliably actuatable in response to extremely small variations in back pressure levels. Because of this, the mechanical device utilized for maintaining contacting engagement with the properly tensioned thread may be of a very lightweight construction, loosely received within its guiding and supporting means. The valving action achieved by the thread detecting device can be of minimum efficiency, enabling substantial clearances to be provided throughout the device, to assure substantially frictionless operation. Moreover, the

utilization of relatively low pressures and the provision for control actuation with minimum changes in such pressures minimizes the effects of the air flow upon the lightweight wire detecting element, such that is remains free to respond by the action of gravity, in the event of a break or discontinuity in the thread.

Because of the loose fitting characteristics of the detecting wire within the detector body, and the constant flow of control air through the device, the critical areas of the detector are substantially self-cleaning of airborne lint. With more conventional devices gradual accumulations of lint eventually can foul the device and render it inoperative. The ability to utilize fluidic control at the appropriate thread break detecting locations enables the necessary electrical control components to be placed at a remote location, in a less hostile environment. In addition, it is possible to completely eliminate the use of mercury pool devices in the vicinity of the machine operator, under conditions which are poorly suited to the reliability and functioning of such devices and which can result in exposure of the operator to toxic mercury vapors. In addition to the many operating advantages of the new fluidic detecting device, as compared to the conventional mercury pool device, the new device also results in significant cost savings, including a substantially lower initial cost.

It will be understood, of course, that the specific form of the invention herein illustrated and described is intended to be representative only, as certain changes may be made therein without departing from the clear teachings of the disclosure. Accordingly, reference should be made to the following appended claims in determining the full scope of the invention.

I claim:

1. A fluidic system for sensing thread break in a sewing system, which comprises a. a source of fluid under pressure,

b. a position sensor fluidic device connected to said source and having a fluid-discharging sensing port,

c. said position sensor fluidic device having a first operative condition when its sensing port is exposed to relatively low fluid pressure and a second operative condition when said sensing port is exposed to relatively higher fluid pressure,

d. a fluidic thread break detector body connected to said fluidic device,

e. said detector body having a control port connected to the sensing port of said position sensor fluidic device,

f. said detector body having therein a relatively free flow fluid passage connected to the control port,

g. said detector body having a vertical guide passage therein having a preselected bore dimension intersecting with said fluid flow passage,

h. means, including a pair of spaced thread guides located above and on opposite sides of said vertical guide passage, for guiding a thread under sewing tension along a predetermined path above said guide passage,

i. a vertically disposed thread detecting wire loosely and slideably received in said vertical guide passage and movable from a first position, supported by a thread under sewing tension and fully retracted from said free flow passage, to a second position, resulting from a thread break. in which at least a portion of the wire is projected through said free flow passage,

j. the presence of said wire in said free flow passage in said second position, resulting in a low efficiency restriction therein and thus in a relatively increased pressure at the sensing port of said position sensor fluidic device, to cause said device to be changed to its second operative condition.

2. A fluidic thread break sensing system according to claim 1, further characterized by a. said thread detecting wire being generally of inverted U-shaped configuration,

b. one leg portion of the wire being received in said guide passage, and

c. said detector body including means for freely slideably guiding the other leg portion of the wire to maintain said wire in a predetermined orientation.

3. A fluidic thread break sensing system according to claim 2, further characterized by a. said detecting wire having a downwardly bent hooklike portion at its upper end providing a pair of laterally spaced suspension points for said wire.

4. A fluidic system for sensing thread break in a sewing system, which comprises a. a thread break detector including a detector body having at least one vertically disposed guide passage formed therein having a preselected bore dimension, and a control air passage intersecting said guide passage,

b. means, including a pair of spaced thread guides located above and on opposite sides of said guide passage, for guiding a thread under sewing tension along a predetermined path above said guide passage,

c. a thread suspended sensing element having at least one vertically disposed portion received loosely, freely and substantially frictionlessly in said guide passage,

d. said sensing element engaging said thread at a plurality of spaced points,

e. said sensing element being of an invented U- shaped configuration and normally thread-suspended by a thread under sewing tension with a depending portion of the U-shaped configuration of its lower end above the point of intersection of said control air passage and said guide passage and being movable by gravity, when released from a thread under sewing tension, to a position with its lower end below said point of intersection,

f. said sensing element, when in its released position,

forming a low efficiency restriction in said air passage,

g. an air line supplying control air to said air passage,

a position sensor fluidic device having its control port connected to said air line and to said control air passage and actuatable from one operative condition to another in response to a relatively slight change in pressure in said control air passage.

5. A fluidic system according to claim 4, further characterized by a. said sensing element comprising a wire having a diameter of on the general order of 0.030 inch,

b. said guide passage having a diameter of on the general order of 0.052 inch, and

c. said air passage having a diameter of on the general order of 0.052 inch.

6. A fluidic system according to claim 4, further chracterized by a. said sensing element comprising a wire-like element.-

of said legs,

e. said second vertical passage being larger in relation to said other leg than said first vertical passage in relation to said one leg. 

1. A fluidic system for sensing thread break in a sewing system, which comprises a. a source of fluid under pressure, b. a position sensor fluidic device connected to said source and having a fluid-discharging sensing port, c. said position sensor fluidic device having a first operative condition when its sensing port is exposed to relatively low fluid pressure and a second operative condition when said sensing port is exposed to relatively higher fluid pressure, d. a fluidic thread break detector body connected to said fluidic device, e. said detector body having a control port connected to the sensing port of said position sensor fluidic device, f. said detector body having therein a relatively free flow fluid passage connected to the control port, g. said detector body having a vertical guide passage therein having a preselected bore dimension intersecting with said fluid flow passage, h. means, including a pair of spaced thread guides located above and on opposite sides of said vertical guide passage, for guiding a thread under sewing tension along a predetermined path above said guide passage, i. a vertically disposed thread detecting wire loosely and slideably received in said vertical guide passage and movable from a first position, supported by a thread under sewing tension and fully retracted from said free flow passage, to a second position, resulting from a thread break, in which at least a portion of the wire is projected through said free flow passage, j. the presence of said wire in said free flow passage in said second position, resulting in a low efficiency restriction therein and thus in a relatively increased pressure at the sensing port of said position sensor fluidic device, to cause said device to be changed to its second operative condition.
 2. A fluidic thread break sensing system according to claim 1, further characterized by a. said thread detecting wire being generally of inverted U-shaped configuration, b. one leg portion of the wire being received in said guide passage, and c. said detector body including means for freely slideably guiding the other leg portion of the wire to maintain said wire in a predetermined orientation.
 3. A fluidic thread break sensing system according to claim 2, further characterized by a. said detecting wire having a downwardly bent hooklike portion at its upper end providing a pair of laterally spaced suspension points for said wire.
 4. A fluidic system for sensing thread break in a sewing system, which comprises a. a thread break detector including a detector body having at least one vertically disposed guide passage formed therein having a preselected bore dimension, and a control air passage intersecting said guide passage, b. means, including a pair of spaced thread guides located above and on opposite sides of said guide passage, for guiding a thread under sewing tension along a predetermined path above said guide passage, c. a thread suspended sensing element having at least one vertically disposed portion received loosely, freely and substantially frictionlessly in said guide passage, d. said sensing element engaging said thread at a plurality of sPaced points, e. said sensing element being of an invented U-shaped configuration and normally thread-suspended by a thread under sewing tension with a depending portion of the U-shaped configuration of its lower end above the point of intersection of said control air passage and said guide passage and being movable by gravity, when released from a thread under sewing tension, to a position with its lower end below said point of intersection, f. said sensing element, when in its released position, forming a low efficiency restriction in said air passage, g. an air line supplying control air to said air passage, h. a position sensor fluidic device having its control port connected to said air line and to said control air passage and actuatable from one operative condition to another in response to a relatively slight change in pressure in said control air passage.
 5. A fluidic system according to claim 4, further characterized by a. said sensing element comprising a wire having a diameter of on the general order of 0.030 inch, b. said guide passage having a diameter of on the general order of 0.052 inch, and c. said air passage having a diameter of on the general order of 0.052 inch.
 6. A fluidic system according to claim 4, further chracterized by a. said sensing element comprising a wire-like element, b. said wire-like element having a pair of vertically disposed, parallel, downwardly extending legs, c. one of said legs being received in said guide passage, d. said detector body having a second vertical passage therein loosely and freely receiving the other of said legs, e. said second vertical passage being larger in relation to said other leg than said first vertical passage in relation to said one leg. 